Tree Functional Group Richness and Landscape Structure in a Brazilian Tropical Fragmented Landscape

This study explores the relation between landscape structure and tree species richness in a tropical area suffering deforestation since the second half of the 19th century. Three different null hypotheses were tested: (1) there is no relationship between landscape structure and tree species diversity present in fragments because the process of fragmentation in these landscapes is too recent to result in tree species extinction; (2) species characteristics do not influence the relationship between tree richness and landscape structure; (3) scale of analysis does not influence the relationship between tree richness and landscape structure. I studied 11 fragments of mesophytic semideciduous forest occurring along the Jacaré-Pepira river (southeast Brazil). From a classified Thematic Mapper image, the landscape structure was quantified using parameters of fragment structure, forest arrangement, landscape complexity, and landscape composition. To investigate the influence of scale over tree species richness, forest and landscape parameters were evaluated around the studied fragments for three different landscape extents. Each forest fragment community was divided into functional groups according to species dispersal capability and shade tolerance, to distinguish possible differences in landscape perception. The relationships between landscape and community parameters were evaluated with regression and discriminant analyses. Results showed significant relations between landscape parameters and species diversity. The nature of these relations changed according to the group and to the landscape extent considered, supporting the view that species perceive the landscape structure differently. The influence of landscape appears to be stronger for shade-tolerant, zoochorous, and barochorous species. Shade-tolerant species were particularly influenced by the fragment structure (connectivity). Zoochorous species were particularly sensitive to landscape parameters at broad scales, whereas barochorous species responded mainly to landscape structure at fine scales. These results attest to an influence of the present landscape structure on the tree community, although the time lag of extinction occurring for long-lived trees may be longer than one century. Furthermore, results showed that boundary complexity and fragment connectivity were the most important parameters of landscape linked to the functional group richness and to total diversity, attesting to the importance of the matrix structure in the relationships between landscape and fragmented communities.